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IC 


8902 



Bureau of Mines Information Circular/1982 



;uv ^ ^ vKC 




A Review of Methods for Identifying 
Scrap Metals 



By R. Newell, R. E. Brown, D. M. Soboroff, 
and H. V. Maker 




UNITED STATES DEPARTMENT OF THE INTERIOR 



'-"mm 



Information Circular 8902 



A Review of Methods for Identifying 
Scrap Metals 



By R. Newell, R. E. Brown, D. M. Soboroff, 
and H. V. Makar 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



As the Nation's principal conservation agency, the Department of the Interior 
has responsibility for most of our nationally owned public lands and natural 
resources. This includes fostering the wisest use of our land and water re- 
sources, protecting our fish and wildlife, preserving the environmental and 
cultural values of our national parks and historical places, and providing for 
the enjoyment of life through outdoca: recreation. The Department assesses 
our energy and mineral resources and works to assure that their development is 
in the best interests of all our people. The Department also has a major re- 
sponsibility for American Indian reservation communities and for people who 
live in Island Territories under U.S. administration. 

1 \N Uii^ 



.114 



This publication has been cataloged as follows: 



A Uevicw of methods for identifying scrap metals. 

(Information circular U.S. Ocpt. of the Interior, Bureau of Mines ; 
8902) 

Bibliography: p. II 

Supt. of IX>cs. no.: I 28.27:8902. 

I. Scrap metal s— Identification. . h Newell, R. (Raymond). II. Se- 
ries: Information circular (United Stales. Bureau of Mines) ; 8902. 



-4M»J^5rt)+ ITS2141 622s 1669'. 042] 82-600249 



{■'or sale by the Superintendent of Documents, U.S. Government Printing Office 
Washington, O.C. 20402 



CONTENTS 



Page 

Abstract 1 

Introduction 1 

Sorting strategy 2 

Preliminary sorting 2 

Object recognition 2 

Color 3 

Weigiit 3 

Magnet testing 3 

Spark testing 4 

Chemical spot tests 5 

Combining simple sorting methods 6 

Optical emission devices 6 

X-ray emission devices 8 

Thermoelectric instruments 9 

Eddy current testing 10 

Quantitative chemical analysis 11 

Other potential methods 11 

Colorimetry 11 



Page 

Ultrasonic inspection 12 

Acoustic emission 12 

Magnetic permeability 13 

Magnetic susceptibility i3 

Infrared emission 13 

Galvanic measurement 13 

Summary 13 

References 14 

Appendix A. — Suppliers of metals identification 

instruments 15 

Appendix B. — Features of optical emission devices 

listed in appendix A 16 

Appendix C. — Features of X-ray emission devices 

listed in appendix A 17 

Appendix D. — Features of thermoelectric devices 

listed in appendix A 18 

Appendix E.^<:)omparison of metals identification 

instruments and identification methods 19 



ILLUSTRATIONS 

1 . Schematic representation of spark testing terminology 4 

2. Arrangement for electrographic sampling 5 

3. Optical prism spectroscope 7 

4. Schematic representation of basic thermoelectric sorter 9 

5. Color variations with composition for high copper content copper-zinc binary alloys 12 

TABLES 



1 . Preliminary identification of metals and alloys by color 3 

2. Preliminary identification of metals by weight 3 

3. Preliminary identification of metals and alloys by magnetic response 3 

4. Spark stream characteristics of metals and alloys 5 

5. Spark stream colors of metals and alloys 5 



A REVIEW OF METHODS FOR IDENTIFYING SCRAP METALS 

By R. Newell,' R. E. Brown," D. M. Soboroff,^ and H. V. Makar^ 



ABSTRACT 

As part of the Bureau of Mines program for conserving domestic mineral resources, a 
survey was made of the methods used for identifying scrap metals. Because of the large 
number of alloys currently being scrapped, correct identification of these materials is 
essential if they are to be recycled effectively. The methods and instruments used to 
identify scrap metals are described and evaluated. These include object recognition, color, 
density, magnetic testing, spark testing, chemical spot testing, thermoelectric measure- 
ments, eddy current measurements, and elemental analysis by chemical and instrumental 
methods. Other potential techniques are discussed also. 

INTRODUCTION 

Large quantities of scrap metals are discarded each year by industry and householders; 
recycling of these materials results in conservation of dwindling domestic resources and 
helps ease U.S. dependence on imports. Substantial energy savings are also achieved by 
increased use of recycled material (18).^ 

In order for these scrap metals to be returned to those operations where they can be 
recycled effectively, they must first be sorted and segregated into lots that contain similar 
materials. The first and most critical phase in this operation is the identification of the metal 
or alloy. 

In the routine operation of a commercial scrap yard, identification and segregation is 
carried out by experienced scrap sorters. The degree of separation the scrap metals 
receive at the scrap yard depends on the abilities of these sorters to identify the alloys with 
which they come into contact. This is commonly done by object recognition or by a limited 
number of physical or chemical tests {1, 9, 16-17, 25, 27, 30, 32-33). 

A widening variety of new alloys now is entering the scrap market, making recognition 
increasingly difficult, even for the experienced sorter. The problem is compounded further 
by the decreasing number of available, skilled scrap sorters. This skill in recognition can be 
achieved only through day-to-day, hands-on experience in the scrap yard or plant. 

Many of these newer alloys are chemically complex, so recycling of these alloys would 
be greatly facilitated if they were separated as discrete alloys rather than as a group of 
alloys with a common base. In fact, separation into discrete alloys is the ideal situation for 
all recycling operations, as it would enable recycling to be achieved without the expense of 
refining, diluting, and realloying. This in turn would maximize the financial return to the 
dealer. 

Identification of scrap may be accomplished by object recognition and by considering 
color, apparent density, magnetic properties, nature of sparks resulting when a metal or 
alloy is touched to a grinding wheel, chemical spot tests, and by the more time-consuming 
methods of chemical and spectrographic analysis. Some of the commercially available 
devices include fluorescent X-ray spectrographic analyzers, portable optical emission 
devices, and thermoelectric sorters. In addition, a number of techniques used in other 
fields of testing may have the potential to identify and sort certain metals and alloys. 

The purpose of this report is to review both currently available and potential methods of 
scrap metal identification. Within the various techniques, a number of commercially 
available instruments are noted. It should be emphasized that these are not intended to be 
complete lists, but are included to inform the reader of the types of equipment commercially 
available. Also, reference to specific company or trade names does not imply endorsement 
by the Bureau of Mines. Similarly, omission of specific company or brand names does not 
imply disapproval by the Bureau of Mines. 



' Lecturer, School of Metallurgy, South Australian Institute of Technology, Adelaide, South Australia; work done while on sabbatical at the Avondale Research 
Center, Avondale, Md. 
^ Physical scientist, Division of Ferrous Metals, Bureau of Mines, Washington, D.C. 
^ Group supervisor, Avondsie Research Center, Bureau of Mines, Avondale, Md, 
' Research supervisor, Avondale Research Center, Bureau of Mines, Avondale, Md. 
^ Italicized numbers in parentheses refer to items in the list of references preceding the appendixes. 



SORTING STRATEGY 



Scrap metals are normally classified into three categories: 
home scrap, prompt industrial scrap, and obsolete scrap. 
Home scrap is generated within the melting or processing 
facility and is recycled back into the melting furnaces. Prompt 
industrial scrap, which is normally generated within fabricat- 
ing and manufacturing operations, may be recycled back to 
the melting and refining facilities if care is taken to keep it 
segregated and free of contamination. Obsolete scrap (or 
postconsumer scrap) is old scrap generated at the end of the 
product life cycle. This material presents the major problem 
for identification and segregation. 

Prior to sorting of scrap, it is necessary to select the groups 
into which the various materials are to be sorted. There is a 
very large number of commercial alloys available and, this 
number is increasing substantially as new alloys come onto 
the market. This wide variety of alloys makes it a practical 
impossibility to separate all scrap into distinct alloys. As a 
result, much scrap is sorted into more broadly based groups. 
The sorting method used needs to be tailored to enable the 
required separation with the highest efficiency. 

Standard classifications for nonferrous scrap and for iron 
and steel scrap have been published by the National 
Association of Recycling Industries (NARI) (29) and by the 
Institute of Scrap Iron and Steel (ISIS) (16). These 
designations are made on the basis of the fchemical 
composition and the physical condition of the material. They 
serve as a good basis for sorting scrap into marketable 
materials, and cover those items that are traded most 
frequently. Classifications other than those published by 
NARI and ISIS are also used. 

The following are examples of classifications: 

ISIS No. 209:— No. 2 bundles: Old black and galvanized 
steel sheet scrap, hydraulically compressed to charging box 
size, and weighing not less than 75 lbs per cubic foot. May 
not include tin- or lead-coated material or vitreous enameled 
material. 

NARI Honey: — 26-yellow brass scrap: Brass castings, 
rolled brass, rod brass, tubing, and miscellaneous yellow 
brasses including plated brass. Must be free of manganese 
bronze, aluminum bronze, unsweated radiators or radiator 
parts, iron, and excessively dirty and corroded materials. 

When deciding on the categories into which a material is to 
be sorted, the economics of the operation is of major 
importance. From a dealer point of view, it is best to sort into 



those categories that will result in the greatest dollar return. 
This, however, does not always result in separating the most 
valuable or critical groups from the scrap. Other factors such 
as insufficient quantities, difficulties in identification and 
separation may make it economically more viable to 
downgrade some of the more valuable or critical materials. 
The more valuable or critical alloys may constitute only a 
small fraction of the total, which, is separated, would be 
insufficient for sale. It may, however, be found that in order to 
meet a given specification, material of higher alloy content 
must be removed or lower grade material must be added to 
dilute the effect of the higher alloy. If sufficient quantities of 
the high alloy material are involved, and if the extra return for 
separating is warranted, then this material would be 
removed. If not, other material must be mixed with the batch 
so that it will meet specifications. 

An example of this can be found within the AISI type 300 
series stainless steels. The NARI classification Sabot 125 
calls for clean 18-8 grade stainless steel clips and solids 
containing a minimum 7 pet nickel and 16 pet chromium and 
a maximum of 0.5 pet molybdenum, 0.5 pet copper, 0.045 pet 
phosphorous, and 0.03 pet sulfur, and othenwise free of 
harmful contaminants. Within this series, type 316 stainless 
steel contains 2 to 3 pet molybdenum, and certain 
less-common grades also have significant amounts of 
molybdenum. In order to meet the specification, these grades 
must constitute less than 10 to 15 pet of the total; othenwise, 
they must be removed or diluted. In this ease, the higher 
molybdenum grades will usually bring a higher price due to 
the high cost of molybdenum, and it becomes economical to 
separate the molybdenum grades from the others, provided 
enough material is available to make up a salable parcel. 

The potential reward for separating material into discrete 
alloys increases as the value of the alloy content increases. 
In addition, there is a potential penalty of increasing 
magnitude if contaminating material is present. This is 
especially true for certain superalloys. These often contain 
significant quantities of several alloying elements, and 
elements that may be beneficial to one alloy may be harmful 
to another. For these alloys, therefore, the incentive exists for 
separating into discrete, uneontaminated alloys, and soph- 
isticated identification, separation, and cleaning techniques 
can be justified. For alloys of lower value, this incentive does 
not exist and simpler methods will suffice. 



PRELIMINARY SORTING 



The preliminary process for identifying metals involves 
judgmental decisions on the part of the sorter based on the 
shape, color, and weight of the material. This is often 
followed by testing with a small hand-held permanent 
magnet. These methods are sometimes ail that is necessary 
for adequate segregation. When separating into standard 
classifications, the physical nature and size of the material as 
well as its chemical composition are considered. 

OBJECT RECOGNITION 

Some alloys can be easily identified on the basis of known 
commercial applications. For example, cocks and faucets 
usually made of similar alloys (yellow brass) are quickly 
sorted into a "cocks and faucets" category for resale, also, 
certain valve bodies are typically made of red brass and can 
be sorted by object recognition alone. Thus, if the class of 
alloys from which a particular object is made is known, then 
the sorting process can be greatly simplified. At best, a 
particular designation can be assigned to the alloy; at worst, 
the number of possibilities can be greatly reduced. 



Unfortunately, a great deal of experience is required to 
make effective use of this method. In addition, the amount of 
experience required increases markedly with the diversity of 
the operation, as the number of alloys and objects likely to be 
encountered in a wide-based scrap business is much greater 
than in a small business. As an example of the use of this 
method for identification, stainless steel cutlery will be made 
from AISI types 410, 420, or 440 grades. Similarly, plumbing 
fittings may be made of red brass, semired brass, or yellow 
brass. These brass alloys can be distinguished from each 
other by color and the appearance of their drillings. 

Information regarding uses and applications of alloys is not 
usually presented in this Vvay. More usually, various alloys 
are listed and their applications noted along with chemical 
composition, mechanical properties, etc. Information of this 
sort is readily available in the technical literature (25, 28), 
from industry groups such as the Copper Development 
Association, the American Iron and Steel Institute, the 
Aluminum Association, and from the producers of the various 
types of alloys. This type of information can be used by the 
sorter to aid in identification. 



A wide range of alloys may be used for certain 
applications. This is especially true for the more complex 
alloys and superalloys that are required for high-temperature 
oxidation and corrosion resistance. Alloys of different 
composition can have similar applications, and the use of 
object recognition can serve only to define the material as a 
superalloy, but not make the closer separations into the 
specific alloy. 

COLOR 

A number of metals and alloys have a characteristic color, 
thus visual examination of color can be used to make an 
initial separation. In certain cases, a definite identification can 
be made on this basis. 

When using color to identify metals, it is important that a 
clean, freshly prepared surface of the base metal be 
examined in order to eliminate the effects of coatings, 
corrosion products, dirt, etc. The clean surface can be 
obtained by filing, grinding, drilling, or shearing. If drillings are 
used, it should be remembered that the color of the drillings 
can vary depending on the amount of pressure used to obtain 
the drillings and on the type of drill and bit used. 

The material should be examined in good light but not in 
direct sunlight. Artificial lights are available that will give the 
same characteristics as daylight. It is also important, in all 
cases where identification is made by the color of the break, 
or by drilling or filing, that the examination take place 
immediately. Exposure to the environment, even for a 
relatively short time, may change the color of the metal, 
making identification more difficult. 

A preliminary sorting based on color can be carried out 
according to table 1 . 



Table 1. — Preliminary identification of metals 
and alloys by color 

Color Metal or alloy 

Red or reddish Copper. 

Light brown or tan 90/10 cupronicl<el. 

Dark yellow Bronzes, gold. 

Light yellow Brasses. 

Bluish or dark gray Lead, zinc, zinc alloys. 

White or light gray Nearly all others. 

A close examination of the drillings may allow a separation 
within the groups shown in table 1 . This is especially true for 
the brasses and bronzes. Examination of the drillings should 
be performed on the dull side, as the shiny side will reflect the 
light. This is important when trying to distinguish between 
alloys where the color difference is only slight. In addition to 
color, the type of chip should also be noted. 

The Institute of Scrap Iron and Steel developed a Copper 
Base Alloy Selector Kit as an aid to the identification of 
common brass and bronze alloys in solid form. The kit 
contains drillings taken from 10 known alloys. To utilize the 
kit, a y2-in drill is used to take drillings from the metal to be 
identified. The drillings from the metal are compared with 
those of the kit; both color and type of chip are compared. 
Allowances must be made for color changes of the standard 
drillings owing to oxidation. 

in certain cases, the appearance of a fractured surface 
rather than a cut surface or drillings can be used to make an 
identification. For example, Muntz metal and admiralty metal 
are both used for condenser tubes and both have drillings of 
a golden yellow color. If a fracture surface is examined. 



however, the Muntz metal break will appear brown, while the 
admiralty metal break will exhibit a green cast. 

WEIGHT 

Since metals vary in specific gravity from 1.74 for 
magnesium up to 21.4 for platinum, an initial separation can 
be made on this basis as listed in table 2. 

Separation into the various groups is made by the sorter by 
picking up various objects and classifying them into the 
categories listed in table 2. 

Table 2 Preliminary identification of metals by 

weight 



Weight Metal 

Very heavy Gold, platinum group, tungsten. . . , 

Heavy Lead, silver, molybdenum 

Light Magnesium, aluminum, titanium . . 

Intermediate Nearly all others 



Specific gravity range 



19.3 -21.4 

10.2 -11.3 

1.7 - 4.5 

6 - 9 



As with preliminary sorting by color, it is possible to make 
separations within the groups by a more accurate density 
determination. For example, within the light metal group, 
magnesium, aluminum, and titanium have a specific gravity 
of 1 .74, 2.70, and 4.5 respectively. The addition of alloying 
elements does not significantly affect these values. Thus, 
alloys of each of these three metals may be readily 
distinguished from each other by a simple density determina- 
tion. A piece of the material is taken and weighed. Its volume 
is then determined by placing it in a cylinder of water and 
noting the displacement of water. The density, determined by 
dividing the weight by the volume, is a reliable value for 
sorting purposes. 



MAGNET TESTING 

Magnet testing involves determining whether or not a 
material is ferromagnetic, that is, attracts a magnet. This test 
is made with a permanent magnet that can either be 
suspended over a convenient location or kept in the sorter's 
pocket. The loosely hanging magnet is brought to a vertical 
surface of the test piece. By testing in this way, any 
movement of the magnet toward the test surface will be 
readily detected. 

There are three ferromagnetic metals, iron, nickel, and 
cobalt. Among the alloys, the iron-base alloys are most likely 
to be ferromagnetic, although a few nickel alloys are also 
magnetic. The 300 series stainless steels are inherently 
nonmagnetic in their fully annealed condition. However, even 
small amounts of cold work will cause some of these steels to 
become substantially magnetic. With increasing cold work, 
the magnetic properties change markedly, depending on the 
composition of the metal. Certain iron-containing copper 
alloys are also slightly magnetic. A summary of magnetic 
properties is given in table 3. 

Table 3. — Preliminary identification of metals 
and alloys by magnetic response 



Response 



Metal or alloy 



Strongly magnetic .... Cast iron, steels, 400 stainless steels, nickel, cobalt. 

Slightly magnetic Monel (not K or S monel), aluminum bronze, 

manganese bronze, silicon bronze. 
Nonmagnetic Nearly all others. 



SPARK TESTING 



Spark testing is based on the property of some metals in 
the finely divided state to oxidize rapidly when heated. When 
such materials are ground by a high-speed grinding wheel, 
the fine particles torn loose are oxidized and raised to an 
incandescent temperature through the heat of friction on the 
wheel. Experienced sorters can, by observing the sparks 
produced in this way, use this method to identify various 
metals and alloys. 

The spark test is conducted by placing the material in 
contact with a high-speed portable or stationary bench 
grinder with a surface speed of -7,500 fpm. The specimen 
should be held so that the sparks fly off horizontally. An 
8-in-diam wheel rotating at 3,600 rpm has a surface speed of 
about 7.500 fpm. The surface speed of the wheel is 
important, as the faster the wheel, the larger and longer the 
spark stream and the less pressure is needed. A wheel 
turning at a surface speed of 3,600 fpm requires consider- 
able pressure to obtain a useful trail of sparks, whereas very 
little pressure is required at 7,500 fpm. 

The type of grinding wheel is important and must be suited 
to the types of metal being spark tested. For normal carbon 
and constructional alloys, a Carborundum Aloxite resinold 
wheel is usually used. For identifying other materials such as 
tool steels or stainless steels other wheels may be better 
suited. The grain size of the abrasive in the wheel does not 
seem to be very important. A 30-grain wheel will give 
somewhat less spark than a 60-grain wheel if all other factors 
are equal. 

Possible contamination of the spark from particles retained 
in the wheel from previous tests can be a problem. It is 
important, therefore, that the wheel be dressed clean before 
spark testing. It is likewise important that the surface tested 
should truly represent the bulk material. The specimen must 
be cleaned with a degreasing solvent, emery cloth, or file to 
remove dirt, grease, corrosion products, metallic coatings, or 
any decarburized or carburized layer. In spark testing steels, 
the heat treatment to which the piece has been subjected 
also has an effect on the spark and must be taken into 
account. Hardened steels generally throw a longer spark 
than annealed steels. 

Proficiency in spark testing requires practice in identifying 
the sparks and in reproducing sparking results, so that a 
given material will sfiow the same sparks whenever it is 
tested. To obtain this reproducibility, care should be taken to 
apply the same amount of pressure over the same sparking 
area in each test. Only enough pressure to maintain a steady 
contact between the material and the wheel should be used. 

The lighting conditions should be approximately the same 
for each test if reproducibility of results is to be attained. 
Spark tests should not be made in bright sunlight or in the 
dark. Diffused daylight or artificial light that approaches 
daylight is best. In the descriptions of spark trails, a number 
of terms are used to describe parts of the trail. These are 
listed and shown schematically in figure 1. 

Certain alloying elements impart characteristic and recog- 
nizable variations to the sparks given by a low carbon steel, 
and these variations are used to help identify the various 
alloys. The manner in which these various elements affect 
the spark is summarized in the following: 

Carbon. — The presence of carbon causes characteristic 
bursts in the spark. The higher the carbon content the more 
plentiful and complicated the bursts. It should be noted, 
however, that these bursts can be suppressed by the 
presence of appreciable amounts of certain alloying ele- 
ments such) as silicon and chromium. 

Manganese. — In steels where the amount of other alloying 
elements is small, manganese tends to brighten the spark 
and increase the spray around the periphery of the wheel. In 



Carrier lines 



Carbon bursts 



Continuous 
Disjointed 

Sprigs 

Preliminary 
bursts 
-Main bursts 



Spear points 



^^^ 

^^^ 



Tongues 



Forked tongues 



Figure 1 . — Schematic representation of spark 
testing terminology (1 and 10). 



steels containing moderate or large amounts of other alloying 
elements, the effects of manganese are not visible in the 
spark stream. 

Silicon. — The presence of silicon suppresses the carbon 
bursts. When the silicon content is greater than about 1 pet, it 
causes a pattern of relatively coarse fuzz (consisting of short 
curved lines) with a dark red discoloration close to the wheel. 
This effect disappears in steels containing appreciable 
amounts of other alloying elements. 

Chromium. — Chromium suppresses the stream and the 
carbon bursts and imparts an orange color to the spark. 

/V/c/ce/. — Nickel causes forked tongues to appear in the 
spark. It also suppresses the stream and the bursts slightly, 
although this effect is less than that caused by the presence 
of chromium. 

Tungsten. — Tungsten tends to suppress the effects of all 
other alloying elements upon the spark stream. When the 
tungsten content is between about 1 and 15 pet, it causes 
single bright orange tongues at the ends of the carrier lines. 
The size of these tongues decreases as the tungsten content 
increases. In high tungsten steels, the carbon bursts are 
suppressed altogether. Tungsten also imparts a reddish- 
' orange color to the carrier lines. 

Vanadium. — Vanadium tends to brighten the spark stream 
as a whole. 

Molybdenum. — In steels in which other alloying elements 
are not high, molybdenum causes a characteristic spear 
point at the end of the carrier lines. Where relatively high 
percentages of other elements are present, these sometimes 
have the effect of masking the spear points. 

Descriptions and diagrammatic representations of the 
sparks obtained from various grades of tool steels are 
available (1). Of the commercially important alloys, those 
with iron or nickel base give characteristic sparks. Cobalt, 
tungsten, molybdenum, and titanium also give off sparks. All 
other metals are nonsparking. Brief descriptions of the 
sparks obtained when testing scrap have also been 
published (30) and are given in tables 4 and 5. 

In making the spark test, it is useful to keep on hand a set 
of known standards, representing the types of alloys with 
which the sorter is likely to come into contact, for comparison 
with the unknown samples. 



Table 4. — Spark stream characteristics of metals and alloys 




Material Description of spark system 

Normal carbon steel Heavy dense sparks 18 to 24 in long that travel completely around the grinding wheel. Sparks are white to straw 

colored with main bursts throughout. 
400 series chromium stainless steel Sparks are not as heavy or dense as in normal carbon steel. Sparks are 14 to 18 in long, travel completely around 

the grinding wheel, and are orange to straw colored, ending with a forked tongue. Preliminary bursts and few 

main bursts. 
300 series 18-8 stainless steel Sparks are not as heavy or as dense as those of normal carbon steel. Sparks are 12 to 18 in long, travel 

completely around the grinding wheel, and are orange to straw colored, ending in a straight line with few, if any, 

bursts. 
310 series 25-20 stainless steel The spark stream is thin and from 4 to 6 in long. Sparks are orange to red in color, do not travel around the 

grinding wheel, and there are no bursts. 
Nickel and cobalt high-temperature alloys. The spark stream is thin and about 2 in long. The sparks are dark red in color, do not travel around the grinding 

wheel, and there are no bursts. 

Table 5. — Spark stream colors of metals and alloys 




Material Spark test color 

Nickel Coarse red. 

D nickel Do. 

Z nickel Do. 

Monel Do. 

K monel Do. 

S monel Do. 

Cupronickel Do. 

Nickel silver None. 

Inconels Very dark red. 

Nimonics Do. 

Nichrome Fine orange-red. 

330 stainless (31-15) Coarse orange-red. 



Material Spark test color 

310 stainless (25-20) Fine orange-red turning white. 

309 stainless (25-12) Coarse light orange turning white. 

300 series stainless (18-8) Light and diffused. 

400 series stainless steel Very light and diffused. 

Cobalt Coarse red. 

Tungsten Short yellow-white. 

Tungsten carbide Do. 

Molybdenum Do. 

Titanium Brilliant white. 

Muntz metal (75 pet Ni, 6 pet Cu, 2 Coarse red. 
pet Cr, balance Fe). 




CHEMICAL SPOT TESTS 



Chemical tests used for sorting or final identification of 
materials range from simple tests to show attack or lack of 
attack by specific acids, to more involved spot tests to 
determine the presence or absence of specific alloying 
elements. These spot tests are based on the formation of 
characteristic colors or precipitates of elements when 
reacted with various test reagents. These microanalytical 
tests are basically qualitative in nature, although semiquan- 
titative conclusions for most of the tests that produce color 
reactions can be obtained by comparison with simultaneous 
tests on known metals and alloys. It must also be noted that 
in order for spot tests to be used successfully for metal 
identification, a knowledge of the chemical composition of the 
alloys likely to be encountered is required. 

The lower limit of detectability of an alloying element by 
spot testing is generally between 0.2 and 1 .0 pet, depending 
on the alloying element in question and the base material. 
For visible differences in a spot test, the quantity of the 
element of interest must vary in concentration by a factor of 
at least two, that is, 1 pet to 2 pet to 4 pet, etc. For this 
semiquantitative work, standard alloys are required. 

Spot test procedures are designed so that maximum 
sensitivity and selectivity can be obtained with a minimum of 
chemical and physical operations. As much as possible, 
separation and conditioning reactions are integrated in the 
test procedures so that the final test becomes a unitized 
operation that can be applied directly for the identification of 
the substance in question. 

In some cases the metal must be taken into solution. 
Reactions of given reagents with the solution are then noted. 
Dissolution may be accomplished by allowing reactions to 
take place on the metal surface or by electrographic 
techniques. When dissolution results from reaction on the 
metal surface, it is essential that a clean, degreased surface 
be used. 

The tests are usually run using one of the following 
techniques: 



1 . By bringing together one drop each of the test solution 
and reagent on porous or nonporous supporting surfaces 
such as paper, glass, or porcelain. 

2. By placing a drop of the test solution on a medium 
impregnated with appropriate reagents. 

3. By placing a drop of reagent solution on a small quantity 
of the solid material. 

In the electrographic method, a sample of the material 
being tested is obtained by simultaneously dissolving the 
metal electrolytically and transferring it to a filter paper. The 
filter paper, wet with an appropriate solution that acts as an 
electrolyte, is placed on a clean degreased area of the 
material to be sampled. The material is then connected into 
an electrical circuit as the anode. The cathode is contacted to 
the wet area of the paper allowing a direct current to flow 
through the electrolyte in the paper. The anode material is 
dissolved electrolytically and the cations produced are 
transferred to the surface of the paper in contact with the 
material. This arrangement is shown in figure 2. 



Wetted wKh 
electrolyte 

Sample paper -^ 



v//////. 




/- Aluminum cathode 
/ electrode 



Sample area on 
sample paper 



Anode clip 

Figure 2. — Arrangement for electrographic 
sampling. 



A description of an electrographic sampling device 
designed to sample aluminum alloys was given by Maynard 
and Wilson (27). Electrographic sampling devices are also 
available commercially in spot testing kits. 

Detailed procedures for identification of metals and alloys 
by chemical spot testing have been developed by the 
International Nickel Company (INCO) (17) and by the 
National Aeronautics and Space Administration (NASA) (39). 
The tests developed by INCO have also been published by 
the Department of Defense (10). 

The families of metals and alloys considered by INCO and 
NASA are aluminum and aluminum alloys, copper and 
copper alloys, magnesium and magnesium alloys, nickel and 
nickel alloys, stainless and heat-resisting steels, carbon and 
low alloy steels, and certain pure metals. In addition, the 
NASA system includes titanium and titanium alloys and 
certain tool steels. 

The equipment and manipulations required for spot testing 
are usually simple and the techniques can be learned without 
difficulty. As in any chemical procedure, the user must be 
aware of contamination problems (11) and safety hazards, 
fy/lost procedures can be conducted by a person with no 
chemistry background or experience, however, some of the 
tests are complex and require experience to interpret 
properly. 

In order to perform the spot tests previously referred to, the 
necessary reagents must be purchased or prepared by the 
analyst. The need for solution preparation can be eliminated 
by the purchase of spot testing kits in which the test solutions 
are already provided in plastic dropping bottles. These kits 
are commercially available from a number of manufacturers. 
Replacement solutions are also readily available. Each bottle 
contains enough reagent for between 250 and 1 ,000 tests 
depending on the manufacturer. 

These spot testing kits vary in their range of application 
from tests designed for specific purposes, such as testing for 



molybdenum in order to separate 31 G stainless steel from the 
other 1 8-8 grades, to general purpose kits that are claimed to 
be able to identify the majority of the most commonly used 
alloys. 

The kits involve either electrographic sampling or spotting 
directly onto the metal surface, depending on the manufac- 
turer and the application. For general purpose identification, 
electrographic sampling is usually used, and the kit comes 
complete with an electrographic sampling system. Compre- 
hensive, easy-to-follow instructions are included with the 
general purpose kits. Some of the kits include a set of alloy 
standards, while others have alloy standards available as 
options. 

The spot testing reagents are identified by code numbers 
or code names and not by chemical names so that the sorter 
usually does not know the reactions involved or the nature of 
the chemicals being used. While this is a disadvantage in the 
case of an accident, it helps to make the tests simpler which 
is an advantage for nontechnical personnel who can follow 
the instructions without overly worrying about understanding 
what is happening. 

Some of the suppliers of spot testing kits and chemicals 
used in spot testing are listed in appendix A. 

While separations can be made solely on the basis of spot 
testing results, a preliminary separation on the basis of 
weight, color, magnetic properties, etc., as discussed earlier 
in this report will help reduce the number of steps required by 
reducing the number of possibilities. Many tests involve 
verifying a particular metal or alloy, or separating a given 
material from a mixture. This enables the analyst to establish 
a definite starting point in performing tests, and allows the 
use of only a segment of the systematic procedure. In these 
cases, a conclusion as to the identity of the alloy can be 
derived quickly. Where there is no basis for selecting a 
starting point, the tests can take 30 or 40 min to complete. 



COMBINING SIMPLE SORTING METHODS 



The identification methods that have been discussed up to 
this point may be combined to form a metal identification 
system. The ability to combine these techniques for the 
purpose of metal identification requires experience, both in 
the application of the testing procedures used and in knowing 
the manner in which the various alloys behave when 
subjected to these procedures. In order to help the sorter, a 
number of charts listing many of the alloys and metals 
commonly encountered and indicating the behavior of these 
alloys under test are available. 

The National Association of Recycling Industries (NARI) 
has included a metals identification chart in its "Recycled 
ivietals Identification and Testing Handbook" (30). This chart 
gives the color and magnetic properties of a number of 
materials and also lists their response to nitric acid and 
ammonia. A chart of chemical spot tests for certain metals 
and alloys is also included. It must be noted that not all the 
alloys listed in the identification chart can be separated from 
each other. It is possible, however, to separate into groups 
on the basis of the tests given in the chart. 



The Department of Defense, in its Defense Scrap Yard 
Handbook (10), has produced a reference table for 
identification of metals which is similar to the chart produced 
by NARI. This table also lists the response of a number of 
alloys to nitric acid and ammonia as well as giving color and 
magnetic response. In addition, the table gives nominal alloy 
compositions and lists typical uses of each alloy. The 
Defense Scrap Yard Handtiook also contains a table giving 
color, composition, magnetic properties, sparking properties, 
and chemical spot tests for a number of metals and alloys. 
' Information of this type has also been published by Obrzut 
(32). 

The Institute of Scrap Iron and Steel has produced a 
metals identification chart for identification of common 
copper-base alloys and monels. This chart combines 
magnetic properties, color of drillings, sparking properties, 
and chemical tests to enable identification. Nominal composi- 
tions and typical uses of the various alloys are also listed. 



OPTICAL EMISSION DEVICES 



Under suitable excitation conditions, many metallic ele- 
ments emit light of characteristic wavelengths. By observing 
these emissions, the material may be qualitatively or 
quantitatively analyzed. The steps in emission spectrochemi- 
cal analysis are (1) vaporization of the sample, (2) excitation 



of the vapor to luminescence, (3) resolution of the resultant 
radiation into a spectrum, and (4) observation and analysis of 
the spectrum. 

The usual procedure for vaporization of solid samples 
requires the passage of an electrical discharge between two 




portions of the sample, or between the sample and an 
electrode that does not contain the elements being 
determined. Metal specimens having a flat surface are 
usually subjected to a spark discharge, with a graphite rod or 
piece of the sample material as a counterelectrode. Metal 
powders or chips may be mixed with graphite, briqueted, and 
partially volatilized by spark discharge. The same electrical 
discharge is used to produce the sample vapor and to excite 
it to luminescence. Radiation results from decay of the 
excited states produced. 

To permit analysis, the component wavelengths of this 
radiation are separated and arranged in order of wavelength 
by either a prism or grating. This is done with a spectroscope, 
spectrograph, or spectrometer, using visual, photographic, or 
photoelectric detection, respectively. The use of the spectro- 
scope for the rapid qualitative analysis of complex materials 
is covered in previous Bureau of Mines reports {13, 34-35, 
37). 

A schematic diagram of a prism spectroscope is shown in 
figure 3 (33). 

Spectroscopes can be used for qualitative or at best 
semiquantitative analysis. Qualitative analysis is done by 
systematically trying to find sensitive lines of analysis of the 
supposed components of the alloy. When the lines of the 
spectrum have been identified, the chemical makeup of the 
material can be deduced. Semiquantitative analysis can be 
obtained by comparing the intensities of the lines in the 
spectrum of the sample to the intensities of samples of 
known composition, since the intensity of an observed 
spectral line increases with increasing content of the element 
(31). Semiquantitative analysis of steel can also be 
performed using a method known as the homologous line 
pair method. This empirical method is based on the fact that 
for steels containing a particular alloy content, the brightness 
of a particular spectral line of the alloying element is similar to 
that of a neighboring iron line. Both these lines form what is 
known as a homologous pair and, by consultation with tables, 
an estimate of the alloy content of the steel can be made. 

For semiquantitative analyses or for alloy confirmation, 
comparative spectroscopes, in which the spectrum of the 
sample is compared with that of a standard of known 
composition, may be used. A number of such instruments are 
available commercially. These instruments have two sample 
tables: an analysis sample table that bears the unknown; and 
a standard table that bears a comparison sample, which is 
either a piece containing the nominal contents of the alloy in 
question or a piece of the pure base metal of the alloy. The 
sample and the standard are arced simultaneously with the 
light from both being reflected into the spectroscope. The 
spectra of both appear juxtaposed in the eyepiece allowing 
easy comparison of the two for both position and intensity of 
the spectral lines. 

The limits of detection of a spectroscope depend on the 
instrument, the element being sought, and the base material 
or matrix. In steels, the lower limit of detection for the 
elements chromium, manganese, molybdenum, titanium, 
vanadium, and copper is about 0.2 pet. Cobalt, nickel, and 
tungsten can only be detected above about 1 pet because of 



KEY 

S Slit 
L, Lens 1 
L, Lens 2 
V Viewer 





Collimator Telescope 

Figure 3. — Optical prism spectroscope {33). 



interference from adjacent iron lines. Silicon, aluminum, and 
niobium cannot be detected visually as their main verification 
lines are not in the visible range. Limits of detection in 
nonferrous materials also vary over a wide range. 

Commercially available spectroscopes vary greatly in size 
and mobility, ranging from hand-held portable units to mobile 
units on wheels and up to larger instruments that must be 
installed in either a workshop or a laboratory. 

Concurrent with changes in the mobility of the instrument, 
the sampling needs change. For a portable instrument, no 
sampling of individual pieces is required as the instrument 
can be taken to the material, provided there is a suitable 
power outlet in the vicinity. Little or no surface preparation is 
required, although thick oxide films should be removed. The 
mobile unit can accommodate samples up to the size of an 
ingot, although the sample must be placed on the sample 
stand and this may be more easily accomplished if a sample 
is cut from the material. For the installed units, a sample must 
be cut from the material. Since the sample usually sits on a 
table and is sparked from below, it should have a flat surface. 
For these instruments, therefore, sampling is an important 
factor. Since only a small area is tested, the homogeneity of 
the material also affects the reliability of the analysis. 

Cleanliness of the electrode is also important. When a 
material is sparked, the vapor generated coats the electrode. 
This takes a finite time to be burned off during the next test. 
Care must be taken, therefore, to ensure that the spectrum 
observed belongs to the material being tested and is not due 
to residual effects on the electrode. 

When the arc is struck, a minute amount of metallic oxide 
fume is given off from the sample surface. However, the 
levels of fume will normally be well below safety limits so that 
no health risks exist to the operator, although it is possible 
that repeated sparking of material containing a high level of 
toxic elements such as lead could produce a problem. In 
addition, the arc formed by the electrode should not be 
viewed directly with the naked eye for a prolonged period. 

Extension of the wavelength range into the ultraviolet 
region is an advantage. The lines of highest intensity are 
usually found in this region. In addition, a number of elements 
have spectral lines that appear only in this region. The use of 
wavelengths down to 200 nm (nanometer) permits detection 
of all metals except small amounts of the alkali metals. 
Because this region is beyond the range of the human eye, 
photographic or photoelectric means must be used to detect 
the spectral lines. 

A relatively new advance in the application of optical 
emission devices to metals identification has been the 
development of small, mobile spectrometers that can be 
moved around yards for onsite testing. The penalty for 
portability is that the sensitivity and resolution possible with 
large, expensive spectrometers is decreased. The capabili- 
ties of the mobile spectrometers are, however, quite 
adequate for alloy sorting and identification. 

The basic operation of the available portable instruments is" 
similar, although the detection capabilities differ. Sparking is 
achieved using a pistol (Aerosol Generator Capillary Arc 
Pistol) that eliminates the need to cut samples from the test 
piece. A direct current arc is ignited between a counterelec- 
trode, located in the front part of the pistol, and the metallic 
sample material. To do this, the end of the pistol barrel is 
placed against the metal, and a single trigger pull initiates a 
low voltage between the electrode and the metal surface. 
The emitted light travels along a fiber optics cable up to 1 m 
long to the entrance slit of the spectrometer optics. The light 
is separated into discrete wavelengths by a grating. Selected 
spectral lines impinge on preadjusted slits with photomulti- 
pliers mounted behind them. In this way, a number of 
elements can be detected simultaneously. 

The portable instruments are strictly comparators. A 
reference standard is sparked and the intensities internally 
stored. When the test material is sparked, the intensities of 
the emission are compared to those of the standard. 



Accordance between test and reference materials within 
preset tolerances is displayed by a green light, differences by 
a red light. Testing takes 10 sec or less and no technical 
experience is necessary. 

These instruments have been designed primarily to verify 
the composition of batches of steel mill products. They can 
be used for final metal identification, particularly if the number 



of possible alloys IS small. They may also be adapted for use 
with nonferrous alloys. 

A number of optical emission devices are commercially 
available that vary greatly in cost and applicability and in the 
experience and skill required to operate them. A list of 
suppliers is included in appendix A. The main features of 
these instruments are summarized in appendix B. 



X-RAY EMISSION DEVICES 



X-rays are electromagnetic radiation of the same nature as 
light, but with much shorter wavelengths, occupying the 
region between gamma rays and ultraviolet radiation. For 
analytical purposes, the wavelength range of interest is from 
0.036 to 2.5 nm. Only the shorter wavelength portion of this 
region is transmitted in air; for wavelengths above about 0.3 
nm, a vacuum path must be used. 

X-rays are produced when high-speed electrons collide 
with a target material. This is normally accomplished in an 
X-ray tube that contains the filament and target in an 
evacuated enclosure. Electrons from the filament are 
accelerated to the target by a high voltage applied across the 
field. This voltage is of the order of 30 to 50 kV. These 
accelerated electrons collide with the metal target and 
produce X-rays at the point of impact. X-rays can also be 
produced using other charged particles, gamma rays, and 
other X-rays. 

If the X-rays generated are sufficiently energetic and are 
used to strike a material, an inner shell electron can be 
ejected from an atom, leaving the atom in a state of high 
potential energy. This is the excitation process. The vacancy 
is quickly filled by an electron from an outer shell, 
accompanied by the emission of an X-ray photon or an Auger 
electron. The energy of the emitted X-ray is characteristic of 
the specific electron transition. 

Some of the X-rays incident on the sample are simply 
scattered by the atoms of the sample, with or without a loss of 
energy. All of the X-rays emerging from the sample form the 
emission spectrum. 

When X-rays are used to excite the atoms of the elements 
in the sample to be analyzed so that their characteristic 
radiation spectra are emitted, the process is known as X-ray 
fluorescence or secondary emission. This is the process that 
was previously described. Alternatively, the X-rays may 
result from the impact of electrons on the surface of the 
sample. This is known as primary X-ray emission. It is also 
possible to use gamma rays for the stimulation of character- 
istic X-rays from the sample. In this case, a radioisotope, 
emitting gamma rays, is substituted for the X-ray tube. 

The irradiation of a sample containing a number of 
elements by an exciting X-ray or gamma ray source results in 
the emission of many characteristic X-ray wavelengths (3-9, 
20-24). In order to analyze the sample, these have to be 
separated. Since all the characteristic X-ray wavelengths 
from the elements are known, identification is possible. 
Moreover, since the intensity of the radiation is a function of 
concentration, it is possible, after suitable calibration, to 
quantitatively determine the composition of the sample 
material. Extraction of the desired information from the 
emission spectrum involves X-ray spectral analysis, data 
processing, and interpretation. 

There are two basic methods of X-ray spectral analysis: 
wavelength dispersive and energy dispersive analysis. 
Wavelength dispersive analysis refers to the separation of 
the X-ray spectrum into wavelengths by using a crystal. This 
is accomplished by allowing the X-rays from the sample to be 
diffracted by a crystal of known interatomic spacing and 
crystallographic orientation. 

Energy dispersive X-ray spectroscopy is a spectral 
analysis technique whereby the X-rays generated from the 



sample are separated and measured by means other than 
crystal dispersion. 

There are three basic types of detectors, with different 
resolutions, used in energy dispersive X-ray spectroscopy. 
The resolution of the system is a measure of the degree to 
which X-rays slightly separated in energy can be disting- 
uished; that is, a measure of the spread of the pulse 
amplitude distribution. The detectors with the best resolution 
are the solid-state detectors. Either lithium-drifted silicon, 
Si(Li), or intrinsic germanium are used. These have 
resolutions of the order of 150 eV at 5,900 eV. They require 
special maintenance, including operation at cryogenic 
temperatures. Solid-state detectors have a broad energy 
detection range. 

Next best in resolution is the gas-filled proportional 
counter, which has a resolution of about 1 ,000 eV at 5,900 
eV. The gas proportional counter is often similar to the 
Geiger counter in construction and filling, except that the 
proportional counter uses a lower voltage and the size of the 
output pulse is proportional to the number of initial ionizations 
caused by a particular X-ray quantum. 

The third type of detector is the scintillation counter that 
has a resolution of approximately 3,000 eV at 5,900 eV. It 
consists of material such as thallium-activated sodium iodide 
that converts a fraction of the X-ray energy into visible light. 
The light is detected by a photomultiplier and transformed 
into electrical pulses. The output pulse distributions from 
scintillation counters are relatively broader (two to three 
times as broad) than those from proportional counters. 
Consequently, there is more overlap of neighboring photons 
and poorer resolution of elements with scintillation counters. 
Pass-band filters (thin foils), which absorb some wavelengths 
more strongly than others, are often used to improve 
resolution when using a scintillation detector. 

The principal advantages of energy dispersive X-ray 
systems are simpler instrumentation and high intensities. 
The major disadvantage of the energy dispersive method of 
^ analysis is the relatively low energy resolution. This results in 
' difficulty in resolving neighboring elements. The resolution of 
elements with two or three atomic numbers between them is 
only partial so that difficulty may be experienced in 
determining minor concentrations of elements. 

As with optical emission devices, large X-ray fluorescent 
spectrometers are in widespread use in the metals industry 
for monitoring the composition of alloys in various stages of 
production. Smaller, less expensive portable or semiportable 
machines are also available, although their detection 
capabilities are reduced (19, 38). These can be used for 
metal sorting and alloy identification in storage yards or in the 
field. Those X-ray emission instruments that have been 
designed specifically for metal sorting and alloy identification 
are comprised of two basic components: a probe and an 
analysis unit. 

The probe, which is often hand held, contains the primary 
radiation source and the detector. Either an X-ray tube or 
radioisotope may be used as the primary source, although 
most modern instruments use radioisotopes. The radioiso- 
topes are often interchangeable, depending on the applica- 
tion, because the range of elements detectable depends on 
the radioisotope being used. Some of the commonly used 



radioisotopes include iron-55, cadmium-109, americium-241 , 
cobalt-57, and curium-244. Field X-ray techniques cannot 
generally be used to determine elements with atomic 
numbers lower than 19 (potassium), although in certain 
cases aluminum and silicon may also be detected. The 
detector also varies from instrument to instrument. Instru- 
ments using crystal dispersion techniques are also available. 

The probe is connected to the analyzer by a signal cable 
which can be up to 50 ft long. The pulse from the detector is 
passed into analog electronics to select for digital processing 
those pulses that represent the specific elements of interest 
to the user. This information is converted into the form 
needed by the operator. 

By the use of microprocessing units in which a number of 
alloy compositions are stored, alloy identification can be 
made by the instrument if the material being tested 
corresponds to one of the stored alloys. The alloy to which 
the sample corresponds is indicated on a display. 

In order for accurate analysis or identification to be made 
by X-ray emission analysis, the instrument must be 
calibrated. Since the aim of X-ray analysis is to determine the 
composition of the sample, it is usually convenient to 
establish a calibration in which the intensity of a characteris- 



tic X-ray line is a function of the concentration of that element 
in a multielement matrix. This calibration is sensitive to 
effects of the other elements present and must be corrected 
for these interelement effects. Because of the sensitivity of 
the method to these matrix effects, only those materials with 
compositions in the range covered by the calibration can be 
accurately analyzed. For materials other than these, the 
instrument must be recalibrated. The calibration may be 
carried out by the supplier in accordance with the user's 
requirements or may be done by the user. 

Certain hazards are associated with X-ray devices. While 
all the instruments commercially available are safe when 
operated correctly, the user must observe all necessary 
safety precautions. In certain cases a Nuclear Regulatory 
Commission license is required. Devices using radioisotope 
sources generally have a shutter over the source which 
opens when the probe is in contact with the sample. 
Malfunction of the shutter could result in a safety problem, for 
the radioisotope sources cannot be turned off, as compared 
to the X-ray tube source. 

The main features of those devices suitable for metal 
identification are summarized in appendix C. A list of 
suppliers is included in appendix A. 



THERMOELECTRIC INSTRUMENTS 



A heated junction between two dissimilar metals will 
produce a potential difference. This is known as the Seebeck 
effect, and is widely used for temperature measurement and 
control. It is the basis of thermoelectric instruments that are 
finding an increasing application in the fields of metal 
identification and sorting. 

The magnitude of the potential difference produced 
depends on the temperature difference between the two 
junctions and on the nature of the metals involved. This 
means that if the temperature difference is held constant, and 
if one of the metals forming the junction is also held 
constant, the potential difference obtained will depend on the 
nature of the other metal in the junction. 

Some alloys will produce potential differences that vary 
greatly from each other, while other alloys will have similar 
readings. This can often be altered by changing the other 
junction material. 

The potential difference obtained depends, in addition to 
temperature and chemical composition, on the physical 
nature of the test material. This presents a problem because 
it means that the potential is sensitive to such things as 
structure, hardness, and surface conditions. Thermoelectric 
measurements are, therefore, sensitive to heat treatment, 
cold working, etc. 

A thermoelectric sorting device measures the potential 
difference between an unknown surface and a heated, 
known surface. Such an instrument must incorporate the 
following features shown schematically in figure 4: 

1 . Two points of contact on the sample. 

2. A heat source so that one point of contact will be hotter 
than the other point of contact. 

3. A sensitive direct current voltmeter, either analog or 
digital, and calibrated either directly in microvolts or in 
relative units. 

There are three ways in which such an instrument may be 
used for metal identification. The first of these is an absolute 
measurement of the voltage, in microvolts, that is generated. 
A table can be constructed listing the microvoltages for each 
alloy that is likely to be encountered. Both chemical 
composition and structure must be considered. In this mode 
of operation the microvoltage is a function of the temperature 
difference between the junctions, and any inaccuracies in 




Test metal 



Figure 4. — Schematic representation off basic 
tiiermoelectric sorter. 



controlling the temperature will produce variations in the 
microvoltage readings. 

In the second method, the voltage is used to generate a 
relative number over the range of alloys likely to be 
encountered. As with the absolute measurement, a table can 
be constructed listing each alloy and temper and its metal 
sorter number. 

The third method is used for confirmation. This requires a 
set of standard samples to calibrate the instrument and a 
standard sample of the alloy being sought. The instrument is 
calibrated for proper operation by checking a standard with 
low thermoelectric voltage and a standard with high 
thermoelectric voltage for proper readings. A verified piece of 
the material sought is then tested and the instrument reading 
adjusted to either zero or some other convenient voltage. 
Any sample that shows a reading other than the set value is 
not of the material being sought. 

The major advantages claimed for thermoelectric identi- 
fication are the speed with which a test can be accomplished 
and the inherent nondestructive nature of the process. 
Because of the geometry of the probes, the junction of the 
two metals is usually small and, hence, the test temperature 
is reached very quickly, provided the instrument has warmed 
up and the probe tip has attained operating temperature. 



10 



After the instrument and probe have come to equilibrium, a 
test can be accomplished in several seconds. The method is 
independent of geometry and mass, provided that the 
matenal is not excessively thin or small, thus no sampling is 
reauired. 

The traditional problem with the thermoelectric process for 
alloy separation is one of controlling the junction temperature 
closely enough to establish a stable, reproducible reading. It 
is electronically possible to resolve a few microvolts at the 
junction at reasonably low temperatures. A change in 
temperature as small as 0.5' C, however, will produce as 
much at 10 to 20 jiV change in output. The junction 
temperature may fluctuate several degrees, even with 
sophisticated control, and this must be compensated for 
electrically. This is complicated both by the difficulty in 
measuring the actual junction temperature, and more 
significantly, each material tested requires a different level of 
compensation owing to differences in thermal conductivity. 

Tfie first commercial instruments using thermoelectric 
effects for alloy sorting were available in the early 1960's. 
Some instruments read out in microvolts, others in relative 
units. Some instruments read out in microvolts, others in 
relative units. Some used copper electrodes for all testing 
while others provided special alloys for various testing 
problems. The method of contact varied from two similar 
probes, to a heated probe and a large ground plate, or a 
heated probe and a large alligator clip. These variations in 
design still exist in the current commercial instruments. 

The manner in which the problem of temperature control is 
treated also varied. There are two main strategies in use, 
although the means by which they are implemented vary. 
The first of these controls the temperature of the probe tip 
and, hence, the hot junction at a given value. The second 
method is to maintain the difference in temperature between 
the hot and cold junctions at a constant value. This latter 
method eliminates the need for recalibration to account for 
changes in conditions. 



An interesting approach to this problem is that of Rowsey 
(36). In this instrument, the need for maintaining a precise 
temperature at the hot junction or a precise temperature 
difference between the probes is avoided by relying not 
simply on the absolute value of the electromotive force 
generated between the probes and the unknown sample, 
but, on the relationship between that value and an electrical 
signal that is indicative of the temperature difference 
between the probes. This latter signal can be derived from 
thermocouples attached to the probe tips. Any change in 
temperature difference between the probes will result in 
variations in both signals. The ratio of the two will be 
substantially constant despite minor variations in the 
temperature difference between the probes and is deter- 
mined by a potentiometric bridge circuit. 

In order to obtain reliable results using thermoelectric 
devices, it is necessary that the surface of the material being 
tested should be clean and free from scale. It is essential that 
the base metal and not a coating be tested, because the 
reading obtained depends on the nature of the material at the 
point of contact with the probe. The surface can be cleaned 
by rubbing with emery paper and wiping off the residue with a 
clean cloth. The probe can become contaminated with 
material from the surfaces with which it comes into contact, 
and should be cleaned periodically. This is especially 
important when testing easily oxidized metals such as 
aluminum. 

The probe tip temperatures of the commercially available 
thermoelectric instruments range from approximately 70° to 
350° C and thus represent a safety hazard. The instruments 
can be operated by personnel with no technical training, after 
instruction in their safe use. 

The operating characteristics of a number of commercial 
instruments are given in appendix D. A list of suppliers 
appears in appendix A. 



EDDY CURRENT TESTING 



An eddy current is a circulating electric current induced 
within the body of a conductor when that conductor either 
moves through a nonuniform magnetic field or is in a region 
where there is a change in the magnetic flux. Typical currents 
of this sort resemble in form the eddies in flowing streams of 
turbulent water, hence, the name eddy currents. Although 
they can be induced in any electrical conductor, the effect is 
most pronounced in solid metal conductors. A suitable 
magnetic field can be generated by a coil carrying an« 
alternating current. This magnetic field will interact with a test 
object brought near to the coil causing eddy currents in the 
test object. These eddy currents in turn create their own 
electromagnetic field, which may be sensed either through its 
effects on the primary excitation coil, or by means of an 
independent sensor. 

In nonmagnetic materials, the secondary electromagnetic 
field depends simply on the eddy currents. With ferromagne- 
tic materials, additional magnetic effects occur that usually 
are much larger than the direct eddy current fields. These 
magnetic effects result from the magnetic permeability of the 
test material. 

The main factors in determining the magnitude and 
direction of eddy currents induced by harmonically varying 
magnetic fields are as follows: 

1 . The geometrical shape of the applied field. 

2. The amplitude of the applied field. 

3. The frequency of the applied field. 

4. The size and shape of the test object. 

5. The location and orientation of the test object with 
respect to the applied field. 



6. The electrical conductivity of the test object. 

7. The magnetic permeability of the test object. 

A very small change in any one of these can have a 
marked effect on the eddy current produced. For practical 
testing purposes, it is usually necessary that all of these 
parameters be rigorously controlled. 

From the point of view of metal identification, the factor of 
most importance is the effect of electrical conductivity. Since 
the electrical conductivity of an alloy is sensitive to changes 
in chemical composition, eddy current techniques can be 
used to identify metals and alloys. Electrical conductivity is, 
however, sensitive to changes in the physical nature of the 
material. This is a complicating factor when this technique is 
applied to scrap metal identification where a given alloy may 
be present in different physical forms. 

Eddy currently test equipment ranges from simple portable 
units to complex automatic or console-type apparatus. 
Regardless of the complexity, however, each system must 
have at least the following elements: 

1 . A source of magnetic field capable of inducing eddy 
currents in conductive materials. 

2. A sensor or transducer, sufficiently sensitive to detect 
the very small changes in the magnetic field caused by eddy 
currents. 

3. A means of interpreting the measured changes in the 
magnetic field, whether it be by monitoring a meter whose 
reading is proportional to the magnetic field change or an 
electronic black box that displays readings proportional to 
phase magnitude or modulation of the magnetic field. 



11 



In simple eddy current instruments, the voltage across the 
coil may be used as a measure of the eddy current effect and 
may be manipulated to produce a meter reading indicative of 
the desired property or feature under investigation. There are 
many variables active in eddy current testing that affect the 
results. In application of this technique to alloy sorting and 
identification, changes in electrical conductivity are usually 
used as a basis for identification. However, the impedance 
values observed can be influenced by heat treatment, grain 
size and orientation, grain boundary precipitation and 
geometrical factors, among others. This means that identi- 
fication of materials may be ambiguous. 

Eddy current testing is rapid, nondestructive, and can be 
substantially automated. In addition, mechanical contact with 
the test article is not normally required, although, in most 
cases, it is necessary to have a flat surface. On the other 
hand, the number of variables that may influence the result 
often make the interpretation of the test results ambiguous. 



The method is restricted substantially to surface analysis 
owing to skin effects, so the presence of coatings, scale, etc., 
presents a problem. When the test articles are ferromagnetic, 
the permeability of the test specimen changes as it is brought 
near to the coil which may obscure the results. 

The eddy current method is best suited to testing large 
numbers of mass-produced articles. The response of a 
standard article may be stored in the memory unit of the 
instrument. The response of the test articles is then 
compared to the stored standard and either accepted or 
rejected. In this way, the articles may be tested for correct 
composition and also for flaws on or near the surface. Eddy 
current testing, at its present state of development, has very 
limited applicability for identification of mixed scrap materials 
owing to the complicating effects of shape and structure. 

A list of manufacturers of eddy current instruments is given 
in appendix A. 



QUANTITATIVE CHEMICAL ANALYSIS 



Positive identification of alloys can be made by performing 
a quantitative chemical analysis and then referring to 
specification tables giving chemical composition for various 
groups of alloys. Often it is necessary to determine only a 
small number of elements in order to identify the alloy, but for 
more complex alloys a more detailed analysis will be 
required. 

Quantitative chemical analysis may be made using 
classical wet analytical techniques, instrumental techniques, 
or a combination of wet and instrumental methods. 

Wet chemical analyses, if performed correctly on properly 
taken samples, are very accurate. They may be, however, 
less sensitive and more time consuming than instrumental 
analyses. When doing wet chemical analysis, it is important 
that standard methods of analysis be used. Standard 
methods for chemical analysis of metals have been 
published by the American Society for Testing and Materials 
(ASTM) (2). These give details of the reagents and 
procedures to be used for determining elements in alloy 
groups. 

A number of instrumental techniques may be used for 
quantitative analysis. These include optical emission analy- 
sis and X-ray analysis, the principles of which have been 
discussed elsewhere in this report. In the context of 
quantitative analysis, the instruments used are, in general, 
larger, more complex, and more expensive than those 
previously described. 

A technique now in widespread use in analytical labora- 
tories is atomic absorption analysis. If light emitted by an 
element inside a special hollow cathode lamp is passed 
through a gaseous cloud containing that element in the 
atomic state, then the atoms of that element, and only that 
element, will absorb the light. In practice, the gaseous cloud 
is formed by aspirating a solution of the sample to be 
analyzed into a flame of sufficiently high temperature to 



reduce the element to its atomic state. The amount of light 
emitted from the lamp that is absorbed by the aspirated 
sample is proportional to the amount of that element present 
in the solution. Comparison with the absorbance of known 
standards enables the amount of the element in the sample 
to be determined. This analysis can be greatly accelerated by 
the use of specially designed graph paper (15) or by means 
of computer programs ( 12). Advances in instrumentation has 
made even more rapid analysis possible. Prior to analysis, 
the sample must be taken into a solution of known volume 
with suitable solvents. For metals, this step is normally 
straightforward. Atomic absorption analysis, when properly 
applied, has few disadvantages and is fairly rapid, accurate, 
and the equipment is comparatively inexpensive. 

A more recent development is the inductively coupled 
plasma optical emission quantometer. These instruments 
analyze samples by producing an aerosol of the sample and 
exciting it in a very stable argon plasma at temperatures from 
2,000 to 1 0,000 K. Diffracted spectral light from the excitation 
is measured as in conventional optical emission devices. 
This method has the advantages of better detection limits 
and the capability of measuring a wider range of emission 
intensities (hence a wider range of concentrations) since 
linear calibration curves are obtained. 

In all quantitative analysis, it is essential that the sample 
being analyzed be truly representative. Sampling proce- 
dures, therefore, are very important. Standard sampling 
methods for various materials have been published by ASTM 
(2) and serve as a guide when sampling scrap material. The 
methods used range from clippings or drillings taken from 
selected pieces to melting a proportion of the material and 
taking drillings from the resultant ingot. In order to ensure 
uniformity of the sample, the sampling method must become 
more complex as the material being sampled becomes less 
uniform in nature. 



OTHER POTENTIAL METHODS 



There exist a number of well-established techniques that 
are used for applications other than metals identification, but 
which could possibly have applications for identifying and 
separating certain metals and alloys. While the manufactur- 
ers of these instruments do not claim that they can be used 
for metals identification, the potential does exist, and this 
report would thus be incomplete without referring to them. 



COLORIMETRY 

Colorimeters are used extensively in the textile, paint, 
food, printing, and similar industries for determining color 
differences with greater precision than the human eye. 
Recent work on the measurement of alloy color has been 
reported {14). This work was directed towards areas where 



12 



alloy color is a desirable property and was designed to 
provide a method of quantifying alloy color and color stability 
in tarnishing environments. 

Perception of color depends on three elements: the light 
source, the object, and the observer. To quantitatively 
characterize the color of an alloy, it is necessary to 
standardize both the light source and the observer. For color 
measurements, the light source is characterized by the 
spectral energy distribution over the optical wavelengths. 
Blackbody light sources are used since their spectral energy 
distributions can be specified by temperature. The standard 
observer is normally a scanning spectrophotometer. 

By itself, spectral energy distribution information in a 
graphical form of reflectance as a function of wavelength is 
difficult to interpret. However, color can be specified in terms 
of numerical indices. The most widely used color system is 
the CIE system (developed by the Commission Interna- 
tionale de r Eclairage). The CIELAB uniform color scale, on 
which the CIE system is based, measures the three- 
dimensional color space components lightness, red-green, 
and yellow-blue. 

It is a fully quantitative system based on opponent colors. 
The units on all three scales are representative of 
approximately equal increments of color difference so it is a 
uniform color space. It is a rectangular coordinate system 
that has a meaningful relation to human visual perception of 



o 

c 

m 

< 

UJ 
O 

O) 

Z 

o 

I- 
< 

< 
> 

cc 
o 

-J 
O 
o 



I00r 



90- 



80- 



COPPER-ZINC BINARY 

~i \ r- 



^ 



•10 



KEY 

■ Lightness - 
A Red-green 
• Yellow-blue 



^ 




I 



10 20 30 

ATOMIC PERCENT ZINC 



40 



Figure 5. — Color variations with composition for 
high copper content copper-zinc 
binary alloys. 



color differences. The lightness, red-green, and yellow-blue 
components are all available as direct readouts from color 
instruments. 

The results of color measurements (14) on a series of 
copper-zinc alloys cast into 10-by 10-by 1-mm paddles that 
were ground and polished before testing are shown in figure 
5. The potential of colorimetry for identification of certain 
copper-base alloys can be readily seen. The potential of this 
method has also been demonstrated by the Bureau of (Vlines 
(26). 

Color measurements are affected markedly by the method 
used to prepare the sample surface. Some of these effects 
are peculiar to certain regions of the color spectrum; whereas 
others are not limited to any particular color region. An 
example of the effect of surface preparation is the amount of 
lead streak produced in alloys containing that element, which 
in turn affects the reflectivity of the metal in the blue regions. 

Besides the need for careful surface preparation, commer- 
cially available colorimeters have two major deficiencies 
when applied to scrap sorting. The sample areas required 
are relatively large because the optical efficiencies of the 
instruments are not high, and the instruments are designed 
for use under laboratory conditions. Both of these may 
possibly be overcome by the use of fiber optics systems for 
the incident and reflected light paths. 

ULTRASONIC INSPECTION 

Ultrasonic inspection makes use of mechanical waves 
above the audible range. Because the ultrasonic waves are 
based on mechanical phenomena, they are particularly 
useful for determining the integrity and structure of materials. 
In addition, ultrasonic energy can be readily introduced into 
materials, and the resulting wave motion is easily trans- 
mitted. 

An ultrasonic beam impinging on an interface between two 
media, for example, the test object and its surroundings, is 
partly reflected and partly transmitted in accordance with 
well-known physical laws. The characteristic that determines 
the amount of reflection is the acoustic impedance which is 
the product of the density of the medium and the velocity of 
the sound waves within it. 

IVIetals and alloys of different compositions have different 
impedances. This then gives rise to a possible identification 
method based on the propagation of ultrasonic waves in the 
material. Such an identification method would, however, be 
greatly affected by the internal structure of the material being 
tested, for example, a flaw can be detected as its impedance 
is different from that of the surrounding materials. 



ACOUSTIC EMISSION 

Acoustic emission is the energy that is released when a 
material is stressed either gradually or suddenly. The energy 
is released in the form of a sound wave that travels through 
the material from the point of origin to the limits of the 
structure. The energy of each pulse is characterized by a 
frequency of about 40 kHz, which is well above the frequency 
of audible sound or vibration. 

The acoustic emission coming from a material under stress 
can be sampled by means of a probe pressed against the 
material. The probe is a transducer, which changes the 
shock wave energy into electrical waves. This electrical 
signal is transmitted to the electrical measuring system which 
rejects the vibration and sound portions of the probe signal 
and amplifies the acoustic emission for measurement and 
display on a decibel meter. The size of the reading for a given 
material is a measure of the strain being produced in the 
metal. 

Because different materials behave differently under 
stress, and because sound waves propagate at different 
rates in different materials, it is possible that acoustic 



13 



emission could be used in metal identification. As with 
ultrasonic methods, acoustic emission is very sensitive to the 
physical and structural condition of the material. The full 
potential of acoustic emission has not yet been realized as it 
is a relatively new field. 

MAGNETIC PERMEABILITY 

The magnetic permeability, \x., is a characteristic parameter 
of a material. It is usually convenient to define another 
quantity, known as the relative permeability, [jlr, as the ratio 
of the permeability of the material to the permeability of 
empty space. Materials may be classified in terms of their 
relative permeabilities. Diamagnetic materials have relative 
permeabilities a little less than unity; paramagnetic materials 
have relative permeabilities a little greater than unity. 
Ferromagnetic materials are those that have relative 
permeabilities considerably greater than unity. 

Magnetic permeability is a function of composition, and, 
thus has some potential as a means of identifying metals and 
alloys. Differences in magnetic permeability are, in fact, used 
in preliminary sorting with a hand magnet, although in this 
case no attempt is made to assign quantitative values to the 
permeability. Unfortunately, magnetic permeability of ferro- 
magnetic materials is greatly influenced by the past magnetic 
history of the material. The permeability of paramagnetic and 
diamagnetic materials is greatly influenced by the presence 
of ferromagnetic impurities. The greatest potential for the use 
of magnetic permeability appears to be in the identification of 
slightly ferromagnetic materials. 



MAGNETIC SUSCEPTIBILITY 

Magnetic susceptibility describes the magnetic response 
of a substance to an applied magnetic field. Since magnetic 
susceptibility varies with composition among other factors, it 
is possible that use could be made of differences in magnetic 
susceptibility for identification. Commercial instruments are 
available for measuring the volume magnetic susceptibility of 
mineral drill cores, hand samples, or outcrops. It is possible 
that they could be adapted for use with metals. 



INFRARED EMISSION 

The infrared portion of the spectrum covers wavelengths 
from about 750 to 10^ nm. These are the wavelengths 
between those of visible light and the microwaves used in the 
highest frequency radar systems. For convenience, this band 
is said to consist of the near infrared (750 to 1 ,200 nm), the 
intermediate infrared (1,200 to 7,000 nm) and far infrared 
(7,000 to 10^ nm) regions. Infrared radiation is naturally 
emitted by all objects because of the thermal agitation of their 



molecules. This motion increases as the temperature of the 
object increases and decreases as the temperature de- 
creases until it stops at absolute zero. Since all molecules 
are made up of electrical charges, the oscillations of these 
molecules cause the radiation of electromagnetic energy. 
The intensity, frequency, and wavelength of this electro- 
magnetic energy are controlled by the temperature and size 
of the source and by the emissivity of the material. The 
emissivity is the ratio between the radiation emitted from a 
body and the radiation emitted from an equivalent blackbody. 
The value of the emissivity varies with the material and the 
surface finish of the body. 

Since the composition of the material affects its emissivity, 
and hence the amount of radiation energy emitted from a 
body at constant temperature, some potential exists for the 
application of emissivity in metals identification. However, 
surface finish and shape play a greater role so careful 
surface preparation would be required. 

Three fundamental types of infrared instruments are 
commercially available. Infrared thermometers make non- 
contact temperature measurements of the object area of 
interest. Process control instruments measure the tempera- 
ture of the object or area of interest and generate a control 
signal to maintain that object or area at the desired 
temperature. Thermographs, also known as infrared camer- 
as, scan a large area of interest and form an image that 
shows the varying amounts of infrared radiation being 
emitted by different parts of that area. These instruments 
could possibly be adapted for metals identification. 

GALVANIC MEASUREMENT 

A difference in electrical potential always exists between 
two dissimilar metals. If these metals are placed in contact or 
othenwise electrically connnected, this potential difference 
produces electron flow between them. The current is a 
function of the composition of the two materials and thus 
provides a method of metal identification. 

A comparative method using galvanic measurements for 
distinguishing type 31 6 stainless steel from Durimet T (22 pet 
Ni, 19 pet Cr, 2.5 pet Mo, 1 pet Cu, balance Fe) has been 
described by the International Nickel Company (17). These 
two alloys cannot be distinguished by standard hydrochloric 
acid and sulfurous acid chemical spot tests because they 
react similarly. In the galvanic method, a known specimen of 
one alloy and the unknown specimen are immersed in a 
1 0-pct HCL solution and are connected to the terminals of a 
to 1 milliampmeter. No permanent deflection of the 
ampmeter needle identifies the known and unknown 
specimens as the same alloy. A permanent deflection of the 
needle identifies the unknown specimen as a different alloy 
than the known specimen. Similar methods could be used for 
other alloys. 



SUMMARY 



A large number of methods and instruments used in 
identifying metals are compared in appendix E. Unfortunate- 
ly, there is no one method or instrument capable of rapid and 
accurate identification of every combination of composition 
and physical condition. Complete chemical analyses, when 
properly performed, will give the required accuracy but 
require long times, a high degree of operator skill, and 
expensive laboratories and equipment. Manual and instru- 
ment methods with the required speed of identification often 
lack accuracy or versatility. 

Most of the identifying instruments have been developed 



for use in confirmation of identity; that is, they are basically 
comparators. They work well in this context to confirm both 
the identity and correct treatment of wrought and cast stock 
and finished articles withing their analytical capabilities. 
When used for scrap identification, complicating factors such 
as changes in the physical character of the material and the 
presence of dirt, grease, platings, and corrosion products 
may affect the operation of the instrument. In addition, the 
need is more for an identifier rather than a comparator, as the 
range of materials likely to be encountered is greater and 
varies more rapidly than in a production situation. These 



14 



problems are greatest for obsolete scrap, as identification of 
prompt scrap may be greatly facilitated by a knowledge of, 
and cooperation with, the source of the material. 

The suitability of the methods and instruments described in 
this report for a given application may be gaged from 



experience and manufacturers' data. Confirmation requires 
testing of appropriate samples. Many manufacturers offer a 
service in this regard and some will dedicate their 
instruments at the factory to fit the customers' requirements. 



REFERENCES 



1. American Iron and Steel Institute. Tool Steel Trends, Winter 
1971. New York, 1971. pp. 2-9. 

2. American Society for Testing and Materials. ASTM Standards. 
Chemical Analyses of Metals; Sampling and Analysis of Metal- 
Bearing Ores, Part 12. Philadelphia, Pa., 1977, 858 pp. 

3. Burkhalter, P. G. Detection Limits for Silver by Energy 
Dispersion X-Ray Analysis Using Radioisotopes. J. Appl. Radiation 
and Isotopes, v. 20. 1969. pp. 353-362. 

4. Burkhalter, P. G. Radioisotopic X-Ray Analysis of Silver Ores 
Using Compton Scatter for Matrix Compensation. Anal. Chem., v. 
43. January 1971. pp. 10-17. 

5. Burkhalter. P. G. Radioisotopic X-Ray Analytical Techniques 
for Gold and Silver Ores. Section in Internal. Atomic Energy Agency 
Pub.. 'Nuclear Techniques and Mineral Resources," Vienna, 1968, 
pp. 365-379. 

6. Burkhalter, P. G. X-Ray Intensity Measurements From Ores 
Using Semiconductor Detectors and Radioisotopic Excitation. Symp. 
on Low Energy X- and Gamma-Ray, Sources and Applications, 
Gordon and Breach, New York, 1971, pp. 147-163. 

7. Burkhalter, P. G., and H. E. Marr III. Detection Limit for Gold by 
Radioisotopic X-Ray Analysis. J. Appl. Radiation and Isotopes, v. 21, 

1970. pp. 395-403. 

8. Campbell, W. J. Applications of Radioisotopes in X-Ray 
Spectrography. Ch. in Radiation Engineering in the Academic 
Curriculum. International Atomic Energy Agency, Vienna, 1975, pp. 
225-258. 

9. Campbell, W. J. Energy Dispersion X-Ray Analysis Using 
Radioactive Sources. X-Ray and Electron Methods of Analysis, ed. 
by William Parrish. Plenum Press, New York, March 1 968, pp. 36-54. 

10. Department of Defense, Defense Supply Agency. Defense 
Scrap Yard Handbook. DSAH4160.1TM755-200, NAVSANDA PUB 
5523, AFM 68-3 MCO P401.2A, June 1966, 204 pp. 

11. Feigl. F. Spot Tests, Inorganic Applications. V. 1, 4th ed., 
Elsevier, Publishing Co., New York, 1954, 400 pp. 

12. Gabler, R. C, Jr., R. E. Brown, and J. G. Haymes. A 
Computer Program for AA Data Processing. Am. Lab., February 

1971, pp. 10-16. 

13. Gabriel, A., H. W. Jaffe, M. J. Peterson. Use of the 
Spectroscope in the Determination of the Constituents of Boiler 
Scale and Related Compounds. Proc. ASTM, v. 47, 1947, pp. 
1111-1120. 

14. German, R. M., M. M. Guzowski, and D. C. Wright. Color and 
Color Stability as Alloy Design Criteria. J. Metals, v. 32, No. 3, March 
1980, pp. 20-27. 

15. Green, T. E. Atomic Absorption Graph Paper. Atomic 
Absorption Newsletter, v. 7, No. 5, 1968, p. 98. 

16. Institute of Scrap Iron and Steel Inc. Handbook. Institute of 
Scrap Iron and Steel, Washington, D.C., October 1979, 110 pp. 

17. International Nickel Co., Inc. Rapid Identification (Spot 
Testing) of Some Metals and Alloys. 1947, 47 pp. 

18. Kusik. C. L., and C. B. Kenahan. Energy Use Patterns for 
Metal Recycling. BuMines IC 8781, 1978, 182 pp. 

19. Lister, D. B. Applications of Energy Dispersive X-Ray 
Fluorescence. Pres. at 21st Annual I.S.A. Analytical Instrumentation 



Symposium, Philadelphia, May 6-8, 1975, pub. in Anal. Instr., v. 13, 
1975, pp. 143-151. 

20. Marr, H. E., III. Mathematical Smoothing of Digitized X-Ray 
Spectra. BuMines IC 8553, 1972, 15 pp. 

21. Marr, H. E., III. Rapid Identification of Copper-Base Alloys by 
Energy Dispersion X-Ray Analysis. BuMines Rl 7878, 1974, 15 pp. 

22. Marr, H. E., III. Six Models for Interelement Correction in 
X-Ray Analysis. Advances in X-Ray Analysis, v. 19, 1975, pp. 
167-180. 

23. Marr, H. E., Ill, and W. J. Campbell. Evaluation of a 
Radioisotopic X-Ray Drill Hole Probe: Delineation of Lead Ores. 
BuMines Rl 7611, 1972, 28 pp. 

24. Marr, H. E., Ill, and W. J. Campbell. The Processing of Energy 
Dispersion X-Ray Data in a Timesharing Computer. Advances in 
X-Ray Analysis, v. 16, 1973, pp. 206-216. 

25. Materials Engineering. V. 90, No. 6, December 1979, 378 pp. 

26. Maynard, A. W., and H. S. Caldwell, Jr. Identification and 
Sorting of Nonferrous Scrap Metals. Proc. 3d Mineral Waste 
Utilization Symp., Chicago, III., Mar. 14-16, 1972, ITT Research 
Institute, Chicago, III., 1972, pp. 255-264. 

27. Maynard, A. W., and D. A. Wilson. Chemical Spot Tests for 
Aluminum Alloys. BuMines Rl 7544, 1971, 15 pp. 

28. Metal Progress. V. 118, No. 1, Mid-June 1980, 202 pp. 

29. National Association of Recycling Industries, Inc. NARI 
Circular NF-80, Standard Classifications for Nonferrous Scrap 
Metals. New York, New York, 1980, 12 pp. 

30. National Association of Recycling Industries, Inc. Recycled 
Metals Identification and Testing Handbook. New York, 1979, 45 pp. 

31 . National Bureau of Standards. Tables of Spectral-Line 
Intensities. NBS Monograph 145, pt. I and II, 2d ed., U.S. 
Government Printing Office, Washington, D.C., 1975, 600 pp. 

32. Obrzut, J. J. Tests That Will Help To Identify Metals. Iron Age, 
V. 221, No. 45, Nov. 13, 1978, pp. 55-58. 

33. Ostrofsky, B. Materials Identification in the Field. Mater. 
Evaluation, v. 36, No. 9, August 1978, pp. 33-39, 45. 

34. Peterson, M. J., and H. W. Jaffe. Visual-Arc Spectroscopic 
Analysis. BuMines Bull. 524, 1953, 20 pp. 

35. Peterson, M. J., A. J. Kauffman, Jr., and H. W. Jaffe. The 
Spectroscope in Determining Mineralogy. The Am. Mineralogist, v. 
32, 1947, pp. 322-335. 

36. Rowsey, J. H., C. E. Snavely, and C. D. Luce (assigned to 
Huntington Alloys, Inc., Huntington, W. Va.). U.S. Pat. 4,156,840, 
May 29, 1979. 

37. Slavin, M. Quantitative Analysis Based on Spectral Energy. 
Ind. and Eng. Chem., v. 10, Aug. 15, 1938, pp. 407-411. 

38. von Alfthan, C, P. Rautala, and J. R. Rhodes. Applications of 
a New Multielement Portable X-Ray Spectrometer to Materials 
Analysis. Advances in X-Ray Analysis, v. 23, Plenum Press, New 
York, 1979, pp. 27-35. 

39. Wilson, M. L. Nondestructive Rapid Identification of Metals 
and Alloys by Spot Test. Technical Support Package for Tech. Brief 
70-10520, NASA Langley Research Center, Hampton, Va., 1973, 78 
pp.; available for consultation at Bureau of Mines Avondale 
Research Center, Avondale, Md. 



15 



APPENDIX A.— SUPPLIERS OF METALS IDENTIFICATION INSTRUMENTS 



Spot Testing Kits 



Company and location 

Chemet Products 
San Francisco, Calif. 
Koslow Scientific Co. 
North Bergen, N.J. 



Company and location 

Agstan Instrument Co. 

Hudson, Mass. 

Analytical Precision Technology Co. 

Coatesville, Pa. 

Applied Research Laboratories 

Sunland, Calif. 

Baird Corp. 

Bedford, Mass. 

Cooperfieat 

Rahway, N.J. 

Spectrex Co. 

Redwood City, Calif. 

Technics 

Springfield, Va. 



Company and location 

Caliber 

Reston, Va. 

Columbia Scientific Industries Corp. 

Austin, Tex. 

Inax Instruments Ltd. 

Ottawa, Ontario, Canada 

Kevex Corp 

Foster City, Calif. 

Pitchford Scientific Instruments 

Canonsburg, Pa. 

Princeton Gamma-Tech 

Princeton, N.J. 

Texas Nuclear 

Austin, Tex. 



Company and location 

Acromag Inc. 
Wixom, Mich. 
Alloy Surfaces Co., Inc. 
Wilmington, Del. 
Analytical Associates 
Detroit, Mich. 
Chemet Products 
San Francisco, Calif. 
Foerster Instruments Inc. 
Coraopolis, Pa. 
Greenberg Engineering Co. 
Bala-Cynwyd, Pa. 
Koslow Scientific Co. 
Edgewater, N.J. 
Technicorp 
Wayne, N.J. 



Company and location 

Foerster Intruments, Inc. 
Coraopolis, Pa. 
Halo Instruments, Inc. 
White Plains, Md. 
Magnaflux Corp. 
Chicago, III. 



Telephone Company and location 


Telephone 


(415)752-5939 Systems Scientific Laboratories (201)482-7734 

Newark, N.J. 
(201)861-2266 


Optical Emission Devices 




Telephone 


Instrument 


(617)562-3219 


Agstan MA/C 


(215)384-1300 


Metals Analyzer 


(213)352-6011 
(617)276-6000 


Quantotest 36000, Horst-Anders 
(Fuess) Metal Spectroscope. 
Spectromobile 


(201)388-4500 


Clandon Metascop 


(415)365-6567 


Vreeland Spectroscope 


(703) 569-7200 


Spectrotest 


X-Ray Emission Devices 




Telephone 


Instrument 


(703)471-1905 


Caliber III 


(800)531-5003 
(512)258-5191 
(613)829-5068 


CSI 740 

Inax 600, Inax 540 


(415) 573-5866 


Kevex Analyst 6600 


(412)745-1555 


Portaspec 


(609)924-7310 


PGT-810, PGT-100 


(512)836-0801 


Alloy Analyzer 9266 


Thermoelectric Devices 




Telephone 


Instrument 


(313) 624-1541 


Metal Tester 1101-B 


(302)575-1555 


ACD-1 


(313)369-9400 


Thermoelectric Comparator TC-78 


(415) 752-5939 


Therm Ergy Meter 


(412)262-2025 


Tevotest 3.205 


(215)839-3380 


Sortometer 


(201)941-4484 


Electrosep 2001 


(201)696-2321 


W.T. Alloy Separator 


Eddy Current Instruments 





Telephone 
(412) 262-2025 

(301) 868-7888 

(312) 867-8000 



Company and location 

Parker Research 
Dunedin, Fla. 
Sensor Corp. 
Scottdale, Pa. 



Telephone 
(813) 733-6081 

(412) 887-4080 



16 



APPENDIX B.— FEATURES OF OPTICAL EMISSION DEVICES LISTED IN APPENDIX A 



Instrument 


Type 


Optical system 


Wavelength Excitation Sampling 


Cost' 








range, nm method 


requirements 




Agstan MA C 


Spectroscope- 


Grating: 1,180 


380-700 Fixed elec- 


Takes material 


$7,000 




comparator. 


lines/mm. 


trodes. 


from wire to 
ingots. 




Metals Analyzer. Mod- 


do 


Prism 


390-700 Fixed elec- 


Small, flat sur- 


$6,000 


el D.V. 






trode. 


face. 




Quantotest 36000 


Spectrometer- 


Grating: ' 2,400 


240-450 Hand-held 


None 


$36,000 




comparator. 


lines/mm. 


pistol. 






Horst Anders (Fuess) 


Spectroscope- 


1 .5 prisms 


420-650 Cu, Fe, or 


C Small, flat sur- 


$13,000 


Metal Spectroscope 
87A. 
Spectromobile 


comparator. 




'390-680 electrodes. face. 




Spectrometer- 


Grating: 1,667 


200-600 Hand-held 


None 


$40,000 




comparator. 


lines/mm. 


pistol. 






Clandon Metascop . . . 


Spectroscope . . 


Amici straight- 


420-650 W or Mo 


do 


$4,000 






vision pnsm. 


'390-650 electrode. 




Vreeland Spectro- 


do 


Grating: 590 


400-700 Fixed elec 


Metal powder . 


$4,000 


scope. 




lines/mm. 


trode. 






Spectrotest 


Spectrometer- 


Grating: ^2,400 


200-760 Hand-held 


None 


$43,000 




comparator. 


lines/mm. 


pistol. 








Mobility 


Size, in Weight, lb Power require- 


Analytical capabilities 








ments 






Agstan MA/C 


Mobile, on 


24 X 24 X 


310 115 V, 60 Hz 


All elements within 


wavelength 




wheels. 


41.5 




range and detection limits. 


Metals Analyzer, mod- 


Fixed 


NA 


NA 220 V, 60 Hz 


Do 




el D.V. 












Quantotest 36000 


Mobile, on 


37 X 24 X 


264 110-220 V, 50- 


Any 10 selected elements. 




wheels. 


26 


60 Hz 






Horst Anders (Fuess) 
Metal Spectroscope 
87A. 

Spectromobile 


Fixed 


NA 


NA 1 1 0-220 V, 50- 


All elements within 


wavelength 
ion limits. 






60 Hz 


range and detect 


Mobile, on 


48 X 34.6 X 


396 110-220 V, 60 


Any 5 elements from 24. 




wheels. 


26.4 


Hz 






Clandon Metascop . . . 


Portable 


13 X 4.7 X 


^17 110-220 V, 50- 


All elements within 


wavelength 






1.8 


60 Hz 


range and detection limits. 


Vreeland spectro- 


Fixed, table top. 


24 X 18 X 


35 1 1 5-220 V, 50- 


Do. 




scope 




16 


60 Hz 






Spectrotest 


Mobile, on 


39.4 X 29.5 


331 110-220 V, 60 


Up to 24 elements 


in groups of 8. 




wheels. 


X 27.5 


Hz 







NA Not available. ' Approximate, subject to change. ^ Paschen-Runge mounting, ' With camera. ■* 20 lb in case. 



17 



APPENDIX C— FEATURES OF X-RAY EMISSION DEVICES LISTED IN APPENDIX A 



Instrument 


Radiation source 


Detector 


Capabilities 


Analytical capabilities 


Caliber III 


. Radioisotope: Cd-109 


Li-drifted Si 


(' 


) 


Elements Ti to U; 


JD to 20 elements 




or Am-241 . 








per determination. Can store 640 












standards. 




CSI 740 


. Radioisotope: Fe-55, 


Proportional counter. Analysis 


. Elements K to U (surface and 




Cm-244, Cd-109, 








sample probes); 


Al to Cr (light 




Am-241. 








element probe), 
groups of 4 per 


32 elements in 
determination. 


Inax 600 and 540 . . . 


. Radioisotope: 1-125. 


Li-drifted Si 


(' 


) 


Elements K to U; from 8 to 36 












elements simultaneously. 


Kevex Analyst 6600 . 


. X-ray tube or 
radioisotope. 


Li-drifted Si 


(' 


) 


All elements heavier than Ti; 19 








elements per determination. Can 












store 175 alloys. 




Portaspec 


. W X-ray tube 


Proportional counter. Analysis . . . . 


. Elements from Ti to Ag and Ba to U. 


PGT810 


. Radioisotope: Cd-109, 


Li-drifted Si or intrinsic C 


) 


Elements from Al to U: Up to 20 




Fe-55, Am-241 , 


Ge. 






elements per determination. Can 




Co-57, and others. 








store 100 alloys 




PGT100 


. Radioisotope: variable. 


Proportional counter or Analysis 


. Maximum of three preselected 




depending on user 


Li-drifted Si. 






elements per determination. 




needs. 












Alloy Analyzer 9266 . 


. Radioisotope: Fe-55 or 


Gain-stabilized 


{' 


) 


Analysis for Cr, Mn, Fe, Co, Ni, Cu, 




Cd-109. 


scintillation counter 




Nb, Mo, W, and Ti or V. Can store 






plus filters. 






100 alloys. 






Cost Mobility 


Electronics 




Probe 


Power 






Size, in 


Weight, lb 


Size, in Weight, lb 


requirements 


Caliber III 


. $45,000 Mobile, on 


NA 


NA 


NA 


NA 


110 V, 5 A, 60 




wheels.^ 










Hz clean 
powerline. 


CSI 740 


. $20,000 Portable . 


NA 


<20 


NA 


NA 


110 V, 60 Hz 














supply or 














battery 














(rechargeable) 


Inax 600 and 540 .. . 


. . $28,000 do . 


12 X 4.5 


16.5 


7.25 


X 4.75 7.5 


Rechargeable 






X 15.75 




X 


10 


battery. 


Kevex Analyst 6600 . 


. . $50,000 Fixed=. ... 


NA 


NA 


NA 


NA 


NA. 


Portaspec 


. . $12,000 Portable . 


"18.5 X 12 

X 9 
NA 


55 


13 X 


4.5 18 
8 

NA 


115 V, 60 Hz. 


PGT810 


. . $40,000 Fixed .... 


NA 


NA 


NA. 


PGT 1 00 


. . $10,000 Portable . 


'9.5 X 11.5 


35 


5 75 


X 4 5 


105-125 V 60 






X 20 




X 


12 


Hz. 


Alloy Analyzer 9266 . 


. . $20,000 do . 


9.5 X 4 X 9 


'8 


7 diam, 2.75 5 
deep 


5 Ni-Cd 
rechargeable 














batteries. 



NA Not available. ' Analysis, 
supply. ' Base. 



matching, identification. ^ Requires dust-free temperature controlled environment. ^ Can have hand-held remote detector. " Power 



18 



APPENDIX D.— FEATURES OF THERMOELECTRIC DEVICES LISTED IN APPENDIX A 



Instrument 



Electrodes 



Probe material 



Control method 



Measurement modes 



ACD-1 Probe and alligator 

clip. 



Thermoelectric 
Comparator TC-78. 



Analog, two sensitivity 
ranges: 1 division — 10 
or 50 |jlV. 

Analog, 1 division — 100 jjlV. 



Analog, 5 sensitivity ranges: 
1 division — 0.9 to 7 |xV. 



Metal Tester Probe and base Cu Constant temperature 

1101-B. plate. difference: 95° to 

145° C. 

W Control tip voltage. 

Temperature 315° 
to 345° C. 

Dual Probes or probe Cu Control tip voltage. 

and ground plate Temperature — 95° C 

for small parts. 

Therm Ergy Meter File, alligator clip. Hard steel file. Operator (file) Analog, alloys identified on 

and pick. Cu clip, and scale, 

steel pick. 

Tevotest 3.205 Probe and alligator Cu, Ni, or Ci-Ni Constant temperature Analog, 5 sensitivity ranges 

clip or probe and alloy. differential — 55° C. 1 division — 1 tp 100 |jlV. 

ground plate. 

Sonometer Probe and base plate. Noncorrosive Constant temperature Analog or digital. 

differential 

Electrosep 2001 File, alligator clip, and Hard steel file, 

pick. Cd-plated steel 

clip, and steel 
. pick. 
W. T. Alloy Probe and alligator Interchangeable 

Separator. clip. probe tips, Cu 

clip. 



Operator (file) Digital. 



Constant tip temper- 
ature— 150° C. 



Analog or digital or 
combined. 



Cost 



Metal Tester 1101-B.. 

ACD-1 

Thermoelectric 

Comparator TC-78 . 
Therm Ergy Meter. . . . 



Tevdtest 3.205. 
Sortometer: 
508 DSE . . . . 



510 

Electrosep 2001 



W. T. Alloy Separator: 
850 



$1,500 

$600 

$1 ,300 

$300 

$4,400 

$6,400 

$1,700 
$500 

$2,700 



Weight, lb 



Power requirements 



Additional comments' 



1 4 Mains power None. 

5 do Do. 

10 do Do. 

^4 Operator (file) Combines thermoelectric and 

turboelectric effects. 
12 Mains power or batteries. None. 

21 Mains power Some models also make use of 

thermal conductivity. 

15 do Do. 

1 Operator (file) and display Sample and hold display, 

(battery). 

10-12 Mains power Models 950 ($2,110) and 

850/950 ($3,460) available. 



' All units are portable. ^ In case. 



trU.S. Government Printing Office : 1982 - 383-884/8706 



19 



APPENDIX E.— COMPARISON OF METALS IDENTIFICATION INSTRUMENTS AND 

IDENTIFICATION METHODS 



Instrument 



Property used 



Analysis Mobility Weight, lb Power requirements 

Qualitative to semi- Portable, mobile, and 20-300 Mains power, 

quantitative fixed units available, 

analysis. 

Comparison of pre- Mobile 300-400 Do. 

selected elements 

for confirmation of 

identity. 
Quantitative analysis, Fixed but may use NA Do. 

alloy matching, hand-held remote 

identification. detector. 
Analysis and in Portable 10-60 Mains power or 

some cases identi- batteries. 

fication. 
Identification by com- do 5-20 Mains power, bat- 

parison with pre- teries, or mecha- 

vious results. nically. 

do do 5-10 Mains power or 

batteries. 
None. 



Spectroscope 

Mobile spectrometer. 



Emission of optical 
radiation of char- 
acteristic 
wavelength. 

do 



X-ray fluorescent Emission of X-rays 
spectrometer. of characteristic 
wavelength. 
Portable X-ray do 

Thermoelectric Production of ther- 
moelectric voltage. 

Eddy current Induction of eddy 

currents. 
Spot tests Chemical reaction . . 



Qualitative or semi- 
quantitative 
analysis. 



Portable kits available. 



1-2 





User skills 


Sample prep. 


Cost 


Advantages 


Limitations 


Safety features 


Spectroscope 


Technical or 


Flat sample from 


$4,000- 


Rapid check for 


Cannot detect 


Arc could cause 




semitech- 


piece. None for 


13,000 


particular ele- 


elements and 


eye damage. 




nical. 


portable units. 




ments. 


emissions in 
UV region. 


Fumes pro- 
duced. 


Mobile spectrometer. 


Semitech- 


Semiclean sur- 


$40,000- 


Rapid nondestruc- 


Limited to con- 


Do. 




nical — none 


. face. 


45,000 


tive identity 
confirmation. 


firmation only. 




X-ray fluorescent 


Technical to 


Sample cut from 


$40,000- 


Rapid quantitative 


Limited to higher 


Potentially haz- 


spectrometer. 


semitech- 


piece. 


50,000 


analysis or 


atomic No. ele- 


ardous radia- 




nical. 






identification. 


ments. Matrix 
sensitive. 


tion source. 


Portable X-ray 


Semitech- 
nical. 


Clean surface. 


$10,000- 
25,000 


Rapid nondestruc- 
tive analysis. 


do 


Do. 


Thermoelectric 


do 


do 


$500- 
6,500 


do 


Structure sensi- 
tive. Different 
materials may 
give same 
readings. 


Hot probe tip 
could cause 
burns. 


Eddy current 


Semitech- 


Clean flat surface. 


$1 ,500 


do 


Structure-shape 


Potential shock 




nical. 




-5,000 




sensitive. Diffe- 
rent materials 
may have simi- 
lar responses. 


hazard may 
exist for some 
models. 


Spot tests 


Semitech- 


Clean surface. 


$50-300 


Usually rapid. 


Sensitive to oper- 


Uses acid and 




nical — none 






essentially non- 
destructive. 


ator interpreta- 
tion. Reactions 
masked by 
other elements. 


other poten- 
tially danger- 
ous chemi- 
cals. 



NA Not available. 










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